The present invention relates to compositions comprising glycerol monoalkyl ethers for use in cosmetic and pharmaceutical preparations and in technical products. These compositions have in particular good long-term storage stability and comprise at least one glycerol monoalkyl ether and at least one antioxidant as stabilizer.
Of the two substitution-isomeric glycerol monoalkyl ethers (2-alkoxy-1,3-propanediols and 3-alkoxy-1,2-propanediols), the present invention relates in particular to the 3-alkoxy-1,2-propanediols.
The invention further relates to concentrates and working solutions. The compositions according to the invention, i.e. in particular the concentrates and working solutions, are added to pharmaceutical and cosmetic preparations and technical products.
Glycerol monoalkyl ethers are used as additives for cosmetic and pharmaceutical preparations and have a multifaceted action. Thus, for example, they are used as physiologically compatible organic solvents. In particular, 3-[(2-ethylhexyl)oxy]-1,2-propanediol (Sensiva® SC 50) has been used increasingly for some years as a deodorant active ingredient and skin care additive in cosmetic and pharmaceutical preparations. Here, the glycerol monoalkyl ethers are added to the preparations or technical products usually in the form of a concentrate or as a pure glycerol monoalkyl ether.
During manufacture, storage and use, the glycerol monoalkyl ether, its concentrate and its dilute solution (working solution) are subject to high requirements which arise from the increased demands of the consumer on the quality of cosmetic and pharmaceutical preparations.
The glycerol monoalkyl ethers are largely chemically stable and stable to external atmospheric influences. They are often colourless, almost odourless liquids and, because of their good chemical stability, are highly compatible with most cosmetic and pharmaceutical ingredients. Because glycerol monoalkyl ethers occur naturally, even the synthetically prepared representatives of the class of substance are particularly desirable for use in end-products because they are widely accepted by manufacturers of cosmetics and pharmaceuticals and end users.
DE 41 40 474 A1 describes the use of certain glycerol monoalkyl ethers in particular as skin care additive for products from the cosmetic and pharmaceutical and quasicosmetic sector and emphasizes their high chemical stability.
EP 0 599 433 A1 discloses that glycerol monoalkyl ethers exhibit effectiveness against odour-causing Gram-positive bacteria. In this connection, deodorizing glycerol monoalkyl ethers of a specifically low-odour and low-peroxide quality are particularly preferred.
EP 0 593 897 A1 discloses aqueous phosphocholine preparations in which glycerol monoalkyl ethers, i.e. 3-alkoxy-1,2-propanediols and 2-alkoxy-1,3-propanediols, are used as physiologically compatible organic solvents. The pharmaceutical preparations disclosed therein are not storage-stable even in the presence of antioxidants. In EP 0 593 897 A1, the stability is improved by the addition of a buffer.
We have now found that the storage stability, in particular the long-term storage stability (over several months to years), with regard to the peroxide content of preparations comprising glycerol monoalkyl ethers is unsatisfactory. Thus, for example, manufacturers of cosmetics complain that incompatibilities between glycerol monoalkyl ethers and formulation constituents or changes in quality of the end-products have been established. The cause of these losses in quality may inter alia be a formation of peroxide which takes place in the preparations depending on the time and storage. The peroxide content in stored preparations varies comparatively greatly and cannot be calculated (chaotic development of the peroxide number, see Experiments A and A (Alu) in Table 1 in Example 1). Furthermore, the appearance of undesired degradation products of low molecular weight was detected by chemical analysis.
The disadvantages of traditional preparations comprising glycerol monoalkyl ethers arise in concentrated and dilute glycerol monoalkyl ether solutions or finished products and can be summarized as follows:    1. Peroxides in cosmetic and pharmaceutical preparations, in particular skin care compositions, when used on the skin of persons with a predisposition, trigger the clinical picture of Mallorca acne (a light dermatosis).    2. A change in the odour of stored precursors or products or stored glycerol monoalkyl ethers results.    3. A change in the odour of cosmetic products as a result of oxidation of natural fats and oils present therein results.    4. Greying of oil-in-water emulsions comprising glycerol monoalkyl ethers arises as a result of incompatibilities of stored mixtures with ingredients of cosmetics and pharmaceuticals.    5. Degradation products of low molecular weight can be detected by chemical analysis.    6. The abovementioned disadvantages can lead to toxicological expert opinions which have a tendency to be relatively unfavourable for cosmetics and pharmaceuticals which have been prepared using stored glycerol monoalkyl ethers.    7. The mixtures, e.g. glycerol monoalkyl ether concentrates, are usually stored in plastic containers. During storage, permanent deformations of plastic containers have been observed, which is referred to as the neck-in effect. Containers with a severe neck-in effect can no longer be stacked safely.    8. Regular quality control of stored glycerol monoalkyl ethers by the cosmetics and pharmaceuticals manufacturers is technologically laborious, long-term storage of glycerol monoalkyl ethers cannot always be avoided and the disposal of amounts of glycerol monoalkyl ethers which have become unusable causes additional costs.